This invention pertains to polymeric compounds including photographically useful groups, and to photographic elements and processes incorporating said polymeric compounds.
Compounds including photographically useful groups (PUGs) desirably are incorporated in film or paper coatings in an inactive, or blocked, form so that they can be activated during photographic processing. Most commonly, PUGs are released as a function of image formation during the photographic development process. In typical color photographic elements, this is often accomplished by using couplers or competitors which release PUGs, such as development inhibitors or bleach accelerators, as a result of reaction with oxidized developing agent.
This is a useful method of releasing PUGs, but often such imagewise release is not the most advantageous. First, it is often difficult to identify PUG-releasing compounds which simultaneously satisfy multiple photographic requirements. For example, PUG-releasing couplers must form dyes of acceptable hue, must be easily prepared, and must have proper reactivity, chemical stability, and dispersion stability. Second, the release of PUGs in an imagewise fashion can degrade image quality, caused, for instance, by the consumption of oxidized developing agent without image formation. Third, many types of PUGs are preferably released uniformly, and not as a function of image formation.
Non-imagewise release of PUGs by cleavage of a PUG from an immobilizing group or an inactivating group, such as a ballast group, a blocking group or a polymer, is therefore desirable. It would be desirable to have a blocking group immobilize a PUG in a photographic element until the blocking group is released during processing, after which the PUG becomes mobile. An example of this would be a filter dye which is immobilized in a layer until processing, when it is released and washed out of the film. Another example would be an immobilized bleach-accelerator fragment which is released during processing and can then interact with the surface of the silver metal in the photographic element. Yet another example would be a blocked, incorporated silver halide developing agent which is released into the photographic element upon treatment with an activator solution containing a dinucleophile. Clearly, many other types of PUGs could be desirably employed in this manner.
However, PUGs attached to immobilizing groups or inactivating groups through a group subject to simple hydrolysis at a rate which is dependent only on the pH of the medium have been shown in most cases to be inadequate. It is known that if such release occurs rapidly in typical alkaline development processes, then the compounds are likely to be unstable during the natural ageing of the photographic element. Conversely, if such compounds are stable during the natural ageing process, then they are unlikely to be sufficiently reactive under typical processing conditions.
One approach to this dilemma is to devise a release mechanism which is dependent on a specific component in the processing solution, and not on pH alone. In other words, a "trigger" in a processing solution causes the release of PUG. Examples of this are found in U.S. Pat. Nos. 4,877,720 and 4,916,047, which disclose polymeric materials in which a bond to a PUG is broken after a blocking group is reduced by a photographic developing agent. One drawback to this approach, however, is that release occurs only in the presence of a developing agent: release cannot be triggered by a processing solution which does not contain a silver-halide developing agent. Also, such blocking groups must be carefully designed in order to be readily reduced by developing agent. Therefore, the compounds can be complicated and difficult to prepare. Furthermore, one would expect to observe non-imagewise formation of oxidized developing agent when such compounds are present in a photographic element, which would lead to undesirable non-imagewise dye formation in typical color photographic elements.
The ".beta.-ketoester" (strictly, .beta.-ketoacyl) blocking chemistry disclosed in U.S. Pat. No. 5,019,492 has enabled production of stable, inactive blocked compounds from which PUGs are rapidly released upon reaction with a dinucleophile, such as hydroxylamine, under alkaline conditions. These blocking groups have been shown to be stable during natural ageing of photographic elements containing them. Release of PUGs occurs without undesirable production or consumption of oxidized developing agent. However, the most reactive blocking groups are not sufficiently large to act as immobilizing groups, or hydrophobic ballasts, for a PUG. Also, in most cases, substitution of the blocking group with a hydrophobic ballast group substantially decreases the reactivity of the blocking group toward dinucleophiles. Furthermore, these compounds are often crystalline and must be prepared as a dispersion in a photographic element, which introduces difficulties such as unwanted variability in the dispersion-making process and unwanted crystallization of dispersed compounds.
There has thus been a need for a material including PUGs which overcomes the disadvantages of the known materials. It would be highly desirable to provide a material which is capable of timely release of PUG with good stability. It would also be desirable to provide materials incorporating PUGs whose hydrophilicity, dispersibility, and mechanical and other properties can be adjusted to meet various processing needs.